1. Field of the Invention
The present invention relates to an artificial knee joint used to properly restore knee joints significantly deformed by chronic rheumatism, osteo-arthritis, pseudogout, and sudden osteonecrosis or the like.
2. Description of the Related Art
In a conventional artificial knee joint shown in FIG. 6, an inner sliding surface 30 and an outer sliding surface 40 of a tibia component 20 are shaped completely symmetrically, the inner sliding surface 30 and the outer sliding surface 40 make a circular arc having a curvature radius R3 at a front side at a longitudinal section and make a circular arc having a curvature radius R4 at a rear side at the longitudinal section, further, R3<R4 here.
In addition, in other conventional artificial knee joint shown in FIG. 7, an inner sliding surface 31 and an outer sliding surface 41 are formed, which are asymmetrical to a tibia component 21 (see U.S. Pat. No. 6,013,103).
In this artificial knee joint, the inner sliding surface 31 of the tibia component 21 is provided as a concave spherical surface of R9 and a front side of the other outer sliding surface 41 makes a circular arc having a curvature radius R7 and a rear side thereof makes a circular arc having a curvature radius R8, and further, R7<R8 here.
However, the above described conventional artificial knee joint shown in FIG. 6 involves a problem such that a large drag (a contact stress) is generated on a sliding surface by a rotational movement generated between the tibia component and a femoral component upon bending so as to bring about an extraordinary abrasion and a damage of the sliding surface of the tibia component although an R curved surface provided at the front and rear sides of the sliding surface of the tibia component allows a stability in a front-to-back direction of the femoral component upon extending the knee joint.
Further, according to a rotational operation of the femur, the femoral component is lifted along the R curved surface of the tibia component so as to bring about an excess tension to a surrounding ligaments and soft tissue, whereby a bending angle may be sometimes decreased.
In addition, in the conventional artificial knee joint shown in FIG. 7, since an inner condyle of the femoral component is completely held, if a rotational axis of the artificial knee joint is not identical with the rotational axis that is ideal for a living body due to unbalance of a ligament balance of the living body and an inefficient handling of an artificial knee joint replacement operation, a drag (a contact stress) acting on the sliding surface upon bending is made very large, and this causes the extraordinary abrasion and the damage of the sliding surface of the tibia component and further, it is feared that the excess tension is generated around the artificial knee joint and the bending angle is decreased by lifting of the femoral component in a rotational movement.